Linear alpha olefins (LAOS) are widely used in a wide range of applications, such as ethylene comonomers, intermediates in production of surfactants, plasticizer alcohols, synthetic lubricants and oil additives, etc. Recently, with the development of the polyolefin industry, the worldwide demand for alpha olefins grows rapidly. Currently, most alpha olefins are prepared based on ethylene oligomerization. Common catalysts used in ethylene oligomerization mainly include nickel-, chromium-, zirconium-, and alumina-based catalyst systems, and so on. Recently, iron (II) and cobalt (II) based catalysts bearing imino-pyridyl tridentate ligands for catalyzing ethylene oligomerization have been reported respectively by Brookhart's group (see Brookhart M. et al, J. Am. Chem. Soc., 1998, 120, 7143-7144, and WO99/02472) and Gibson's group (see Gibson V. C. et al, Chem. Commun., 1998, 849-850, and Chem. Eur. J., 2000, 2221-2231), in which both the catalytic activity and selectivity of alpha olefins are high.
Prior arts teach that water is rather harmful to ethylene oligomerization. The oligomerization process at present, therefore, demands an extremely anhydrous and oxygen-free environment, in which, however, initiation, stability, and repeatability of oligomerization reactions are difficult or poor.
The present disclosure expects to provide a technical solution that can overcome prejudices against water in the prior art relating to the oligomerization process. When a catalyst composition containing water is provided for ethylene oligomerization, a high oligomerization activity can actually be obtained even at a rather low ratio of aluminum to iron and/or a low temperature.